On the influence of conduction electrons in rare earths on the crystal field state in metals - an investigation by inelastic neutron scattering

The influence of conduction electrons on the crystal-field (CF) potential acting on rare earth (RE) atoms was studied by inelastic neutron scattering. The magnetic RE-atoms Pr, Nd, Tb, Dy, Ho, Er and Tm were doped into the isostructural, non-magnetic lattices LaAl2, YAl2 and ScAl2 with concentrations between 0.1 at-% and 2 at-%. Because of this low concentration the interaction between magnetic moments was supressed and single ion CF-parameters and coupling constants between RE-moments and conduction electrons were determined. The CF-parameters for these RE-ions show a typical curve with a minimum near Dysprosium, similar in the three lattices but characterized by a shift of the curves. The coupling constants show also a minimum for Dysprosium and Holmium and an increase for the light and heavy RE-atoms. A simple model taking point charges and the influence of the conduction electrons into account can give a qualitative explanation of the observed CF-parameters. The relative distance of the CF-parameter curves can be regarded as consequence of point charge influence, whereas the sign reversal for the 4th-order CF-Parameters are ascribed to 5 d-conduction electron contributions, not contributing to 6th-order parameters. Furthermore the concentration dependence of the magnetic ions on the magnetic excitation spectrum was studied and for Tm in LaAl2 the influence of the onset of the superconducting phase on the CF-linewidths. The relaxation behaviour of Ce in CeAg at normal and hydrostatic pressures (2 up to 2.3 GPa) was measured. The observed increase of the quasielastic linewidth with pressure gives a hint to a growing Kondoinstability of the Ce3+ ions in CeAg. (orig.)